TRANSMISSION OF TROPICAL DISEASES. 7 



Of course the two fundamental methods are either (1) killing 

 the parasites in the blood by means of quinine, a method 

 which in Italy has yielded excellent results, or (2) destruction 

 of mosquitoes, or rather their larvae ; this in some places 

 has also given very good results, but frequently it is difficult 

 of performance — at least with the funds available. 



Yellow Fever. 



Is a disease the cause of which is unknown, but we know 

 how it is transmitted, viz., by a particularly annoying mosquito 

 from its persistent attempts at biting — Stegomyia fasciata. 

 We know with regard to the mode of transmission that the 

 mosquito can only transmit if it has bitten a patient not 

 later than the third day of the disease, and that it is able 

 to transmit the disease only twelve days later. That is 

 practically all we know. But there is one mystery about 

 the mode of transmission. Yellow fever is, so far as is known, 

 only contracted at dusk or at night, not in the day time. 

 Yet the Stegomyia bites at all times of the day and night. 

 Only one explanation of this peculiarity has been suggested. 

 It is that young mosquitoes bite in the day and old mosquitoes 

 at night. This change in habits takes place when the mosquito 

 is about three days old, i.e. when she first lays eggs. As the 

 mosquito is only dangerous twelve days after it has bitten a 

 yellow fever patient, no day-biting Stegomyia is ever dangerous. 

 This explanation, however, seems to be too good to be true. 

 The Stegomyia is a so-called domestic mosquito, i.e. it breeds 

 in water supplies about the house, tins, barrels, water troughs, 

 etc., etc. It is surprising what quantities of larvae and pupae 

 a single barrel can produce. They are as thick as tadpoles 

 in a shallow pool. It is this fact, viz., the domestic habits 

 of this mosquito which make it comparatively vulnerable 



